KABUL, Afghanistan (AP) - Last year was the deadliest on record for civilians in the Afghan war, with 3,021 killed as insurgents ratcheted up violence with suicide attacks and roadside bombs, the United Nations said Saturday.

Taliban-affiliated militants were responsible for more than three-quarters of the civilian deaths in 2011, the fifth year in a row in which the death toll went up, the U.N. said.

The figures were a grim testament to the violence the Taliban and allied Islamist militants can still unleash in Afghanistan, even as NATO begins to map out plans for international troops to draw down and give Afghan security forces the main responsibility for fighting insurgents by the end of 2014.

"A decade after the war began, the human cost of it is still rising," said Georgette Gagnon, director for human rights for the U.N. mission in Afghanistan. The number of civilian deaths was up 8 percent over the previous year.

Deaths in suicide bombings jumped dramatically to 450, an 80 percent increase over the previous year. While the number of suicide attacks remained about the same, they killed more civilians. On Dec. 6, a bomber detonated his explosives-filled vest at the entrance of a mosque in Kabul, the capital, killing 56 worshippers during the Shiite Muslim rituals of Ashoura. It was the single deadliest suicide attack since 2008.

The single biggest killer of civilians remained the ever-more-powerful roadside bombs planted by insurgents. The homemade explosives, which can be triggered by a footstep or a vehicle and are often rigged with enough explosives to destroy a tank, killed 967 people - nearly a third of the total.

The 130,000-strong coalition force led by the U.S. says it has been hitting the Taliban hard, seizing their one-time strongholds while expanding and training the Afghan army and police to take over primary responsibility for waging the decade-old war.

Still, insurgent attacks are killing more and more civilians, according to a detailed annual U.N. report.

The increased presence of security forces managed to reduce civilian casualties in the troubled southern provinces of Helmand and Kandahar, but the U.N. said insurgents simply pulled back and focused instead on areas along the country's border with Pakistan, relying more on roadside bombs and suicide attacks in places like bazaars, schoolyards, footpaths, and bus stations.

"The tactics have changed," said Jan Kubis, the U.N. Secretary-General's special representative to Afghanistan. "The anti-government forces being squeezed in certain areas ... move to some other areas and again use these inhuman, undiscriminating weapons like human-activated explosive devices and suicide attacks."

He pointed out that the Taliban itself banned the use of land mines as "un-Islamic and anti-human" in a 1998 proclamation issued while the hard-line movement ruled Afghanistan with their harsh interpretation of Islamic law.

The U.N. report said there is little difference between mines and the buried homemade bombs used by the Taliban. The majority of improvised explosives have about 9 pounds (20 kilograms) of explosives and are triggered by pressure plates rigged to explode when a person steps on it or a vehicle passes over.

"These are basically land mines," Kubis said of the roadside bombs. "So why is this 'inhuman and un-Islamic' weapon being increasingly used?"

The sheer number of roadside bombs that insurgents planted last year overwhelmed security forces' improved ability to detect and neutralize them. An average of 23 roadside bombs per day were either detonated or discovered and defused last year - twice the daily average in 2010, the U.N. report said. Actual explosions increased by 6 percent.

The report's toll of 3,021 civilians dead in violence related to the war and 4,507 more wounded made 2011 the deadliest year for Afghan civilians recorded by the U.N. since it started keeping a detailed count of civilian casualties five years ago. Last year's figure was roughly double the number from 2007.

The U.N. attributed 77 percent of the deaths to insurgent attacks and 14 percent to actions by international and Afghan troops. Nine percent of cases were classified as having an unknown cause.

The number of civilian deaths caused by insurgents was up 14 percent over 2010, the U.N. said, while those caused by security forces went down 4 percent.

Last year was also the second-deadliest year of the decade-long war for international forces in Afghanistan, with at least 544 NATO troops killed. The coalition has been in Afghanistan since the aftermath of the 2001 American-backed intervention to topple the Taliban, which followed the hard-line Islamist regime's refusal to hand over al-Qaida terrorist chief Osama bin Laden, who sponsored the Sept. 11 terrorist attacks on the U.S.

While the total number of civilian deaths caused by international and Afghan forces dropped, the number of civilians killed by air strikes targeting insurgents rose to 187 in 2011, accounting for nearly half the deaths attributed to forces supporting the government.

The number of civilians killed during controversial, coalition-led night raids on homes dropped to 63 in 2011, down 22 percent from the previous year, the U.N. said.

The U.N. noted a shift in where the violence affecting civilians was centered. In 2010, the provinces with the highest numbers of civilian casualties were the southern Taliban strongholds of Helmand and Kandahar, where an increased number of U.S. troops pushed to take back territory from insurgents.

While those two provinces still had the most deaths in 2011, their numbers dropped, while civilian deaths went sharply up in southeastern provinces including Khost and Paktika, and the eastern provinces of Kunar and Nangarhar. All those areas lie along Afghanistan's volatile border with Pakistan, where many of the Taliban's leaders and the al-Qaida-allied Haqqani network are believed to be based.

Insurgents also intensified an assassination campaign against people associated with the Afghan government. The U.N. report documented 495 targeted killings in 2011, including provincial and district officials, peace council members and pro-government tribal elders. Assassinations were up 3 percent from the previous year and up 160 percent from 2009.

Among the highest profile assassination victims last year was former President Burhanuddin Rabbani, head of the high peace council charged with seeking talks with the Taliban. He was killed by a suicide bomber claiming to carry a message from the insurgents.